docs: def open(filename, mode='r', **kwargs):  #pragma: no cover
      """
      open() which supports exclusive mode 'x' in python < 3.3
      """
      if six.PY3 or 'x' not in mode:
          return sys_open(filename, mode, **kwargs)
  
      flags = os.O_EXCL | os.O_CREAT | os.O_WRONLY
      if 'b' in mode and hasattr(os, 'O_BINARY'):
          flags |= os.O_BINARY
  
      fd = os.open(filename, flags)
      mode = mode.replace('x', 'w')
      return os.fdopen(fd, mode, 0x664)